Soil erosion and nitrogen leaching in northern Vietnam: expression and modelling.

In Tam Duong district, erosion and leaching are the main processes leading to high nutrient losses and consequently uneconomic production and soil degradation. Counteracting measures can be designed to reduce these losses, based on knowledge derived from quantitative studies of these processes in the various production systems. To increase insight in the basic processes underlying soil degradation at different spatial scales, our study pursued the following objectives:

- To survey soil degradation dynamics in the study area, using remote sensing, to delineate the extent of different soil degradation types as a basis for the design of effective soil conservation measures.

- To study soil erosion at different spatial scales in the hilly land watershed, effects of paddy fields on soil erosion in the watershed, and to simulate soil erosion in the watershed in the presence of paddy fields.

- To quantify nutrient losses due to leaching from different soils and agricultural systems through field experimentation and to develop a suitable model for estimation of nutrient leaching losses from these agricultural systems.

- To scale-up nitrogen dynamics and leaching losses in a small region, using geostatistics and a geographic information system (GIS).